This study proposes a safe dosing regimen IFN-γ that is sufficient to stimulate IFN-γ receptors on malignant blasts in patients who developed relapsed acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) after alloSCT with no active or history of III-IV acute graft-versus-host disease (GVHD). It is hypothesized that IFN-γ will promote graft-vs-leukemia (GVL) in patients with AML/MDS that has relapsed after alloSCT.

Allogeneic hematopoietic stem cell transplantation (alloSCT) can cure patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). However, relapsed AML/MDS is the most significant single cause of treatment failure, and the majority of relapsed patients ultimately succumb. Alloreactive T cells in the donor graft can kill residual leukemia cells, mediating the graft-vs-leukemia (GVL) effect. Consistent with this, recipients of T cell-depleted grafts have higher rates of relapse. GVL is more potent against chronic leukemias than acute myeloblastic diseases, and the higher incidence of relapse in patients with AML/MDS reflects a failure in GVL.

The central goal of this pilot trial will be to explore whether IFN-γ in this setting is safe and whether it has the desired biological activities on malignant blasts in vivo. IFN-γ will be tested in relapsed patients as monotherapy and in conjunction with donor leukocyte infusions (DLI). The clinical and biological information from this study is essential to design a phase II trial with a therapeutic endpoint.

Treatment will be initiated at 100mcg (almost equal to the dose of 50 mcg/m2 for an adult) three times a week, with the potential to deescalate the frequency of injection for unacceptable toxicity. To explore whether this dosing regimen is sufficient to activate myeloblasts, pre- and post-treatment bone marrow specimens will be harvested to analyze for IFN-γ action (upregulation of HLA class I; HLA class II, ICAM-1 and phosphorylation of STAT1). The primary safety concern is the development of GVHD, which is routinely monitored for all alloSCT patients.

Inclusion Criteria:

• Recipients of allogeneic stem cell transplantation for acute myeloid leukemia or myelodysplastic syndrome from a human leukocyte antigen (HLA) matched donor
• Relapsed of primary disease with 5% to 20% of blasts in the bone marrow by flow cytometry in the bone marrow with an clear leukemia-associated immunophenotype (If the patient received therapy to treat the relapse, he or she must have 5-20% residual blasts prior to enrollment on this study)
• Performance status KPS score >60% (ECOG 0-2)
• No increases in systemic immunosuppression in the prior four weeks other than to maintain therapeutic levels
• No systemic corticosteroid with a dose higher than 0.5mg/kg/day prednisone or equivalent
• No history of grade IV acute GVHD
• No new systemic immunosuppressive medications in the prior two weeks initiated due to GVHD
• Willingness to have bone marrow and peripheral blood collected as per the study protocol
• Must be able to give informed consent
• Age 18 or older

Exclusion Criteria:

• Contraindication to receive IFN-γ including known hypersensitivity to interferon-gamma, E. coli derived products or any component of the product
• Subjects with a positive pregnancy test or who are breastfeeding
• For men or women of childing bearing potential (age < 50 without hysterectomy or oophorectomy or documented menopause), unwilling to use effective contraception for the duration of the study.
• Primary engraftment failure
• Active cardiac arrhythmias not controlled by medical management or current NYHA class II or higher congestive heart failure
• Active ischemic heart disease not well controlled with medications
• A seizure disorder not well controlled by medications
• Estimated GFR <30 mL/min
• AST/SGOT or ALT/SPOT > 5 x ULN
• Total bilirubin > 3 x ULN
• Chemotherapy (other than hypomethylating and/or venetoclax therapy) within the prior 4 weeks
• Body surface area at or less than 1.5 m2, or greater than 2.5 m2 so as to minimize the variation in IFN-γ exposure based on differences in BSA.
• Patients less than 18 years old.
• Pregnant or breastfeeding patients.